Re: What happened between Newton and Einstein?

On Mar 1, 10:19 am, "PD" <TheDraperFam...@xxxxxxxxx> wrote:
I'm sorry, I don't see how absolute motion is
the *only* possible cause of the age differences
between twins and triplets.

In the case of the twins, A and B, A and B *both
agree* that A takes a straighter path through
spacetime than B. However, this in no way implies
anything about absolute motion.

You don't see it because using twins obscures the
truth. You must use triplets to clearly see what
is happening.

Unlike the twin case, the triplet case contains
no turnarounds and no accelerations.

This leaves only motion through space (aka absolute
motion) as the physical cause of the triplets'
age differences.

[kk wrote:]
Re your second claim, I reply that since Einstein's
2nd postulate is purely a mere definition (of clock
synchronization), it cannot pertain to anything in
nature.

I completely disagree. The second postulate is an
explicit statement about what will be the result of
a measurement of the speed of light,

Please describe how this "measurement" can be made.

There is NOTHING in the statement of the second
postulate that says anything about clock synchronization.

Please describe how one can measure light's one-way
speed between points A and B without using two clocks
that have been "synchronized" in some way.

After you have tried to provide this description and
failed, it will then dawn on you that the 2nd postulate
is indeed purely a definition of clock synchronization,
as Einstein said.

That is, you will then see that since it is not
possible to measure light's one-way speed from
point A to point B without two clocks, and you
will also see that the clocks must be related
in some way, you will see that someone must
provide a prescription for how the clocks are
to be related, and this is a definition of
clock synchronization.

However, in Einstein's case, the following problem
arises:

Einstein cannot really (or absolutely) synchronize
clocks, and even if he could, he would not get the
"answer" that he wishes to get, namely, a one-way
"null result."

The only way Einstein could obtain a one-way "null
result" was by forcing clocks to read x/c when a
light ray traveled the frame distance x.

But this is clearly not a measurement; it is only
a stipulated "result," given at the start before
any measurement is made.

This is why you cannot describe the procedure for
the "measurement" that you claimed can happen.

However, the postulate is not dependent on clock
synchronization in any way. In fact, using light
for clock synchronization is not even a *requirement*.
You can synchronize two spatially separated clocks
by *any* procedure that carries a signal at the same
speed in both directions -- including walking. Einstein
just happened to use light because he had just
postulated that it satisfies this criterion as a usable
signal.

Here's Einstein's 2nd postulate:

"Any ray of light moves in the 'stationary' system of
coordinates with the determined velocity c, whether
the ray be emitted by a stationary or by a moving body.

Hence

velocity = light path/time interval

where time interval is to be taken in the sense of
the definition in section 1."

Here's the definition from section 1:

"Let a ray of light start at the 'A time' Ta from A
towards B, let it at the 'B time' Tb be reflected at
B in the direction of A, and arrive again at A at
the 'A time' T'a.

In accordance with definition the two clocks synchronize
if
Tb - Ta = T'a - Tb "

No mention of walking or bullets or baseballs; only light.
Also, note Einstein's use of the word "definition."

The time portion (Einstein's "time interval") of
the 2nd postulate is dependent upon Einstein's
definition of clock "synchronization."

Note that Einstein did not experimentally measure
light's speed during any part of the 2nd postulate.

In fact, no one has ever measured light's speed
from point A to point B.

Einstein merely stipulated that the clocks must
read equal travel times. That is, they were
forced by Einstein to read equal travel times,
so they did not get this result experimentally.

This means that the 2nd postulate really has
nothing to do with physics - it is merely a
definition. It says nothing at all about any
thing in nature. It merely reflects Einstein's
belief that we will never be able to detect
absolute motion. It is a mere artificial
null result, given entirely by man.

In fact, it is impossible to experimentally
obtain a null result in the one-way case.

("one-way case" here means "the direct and
simple measurement of light's one-way speed
between two points without using clocks that
have been transported or rotated because such
clocks run slow.")

[kk wrote:]
Real clock slowing and real rod shrinkage entered
SR not via Einstein's postulates, but via his
upfront (pre-postulation-era) acceptance of the
Michelson-Morley experiment null result. (Actually,
Einstein simply accepted upfront full round-trip
nullness, which included both the MMx and the KTx,
with the former having rod contraction, and the
latter having clock slowing.)

Actually, if you read the histories of this, Einstein was pretty
steadfast in being unaware of the MMX result. However, he was *quite*
aware of the form of Maxwell's equations, and he was *very* aware of
that factor of c that appeared everywhere in them, and he was
*painfully* aware that no absolute speed appears anywhere in any of
the Newtonian laws of motion and that this fact ensures their
invariance with choice of inertial reference frame. And so he simply
tried to figure out how it is possible that c could appear in
Maxwell's equations and still have those equations be invariant with
choice of inertial reference frame. It was Maxwell's equations that
demanded the invariance of c, not the MMX.

I have read the history, and here it is:

[From the 1905 relativity paper]
"In agreement with experience we further assume the
quantity 2AB/(t'a-ta) = c to be a universal constant --
the velocity of light in empty space."

Einstein's "in agreement with experience" means "in
agreement with experiment." And the only experiment
that said "round-trip invariance and isotropy" was
the Michelson-Morley experiment. (footnote: actually,
the MMx said only isotropy; the later KTx added
invariance; this is why Einstein used the word
"assume"; he knew that he was talking about both
isotropy and invariance.)

Maxwell did not measure light's round-trip speed.
Nothing in Maxwell's equations tell us anything
about either light's one-way or round-trip speed.

Try again.

.

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